Plug and play is the name for a number of technologies used in computing. Technologies that support plug and play allow to connect new devices to a computer. After a short while, these devices can simply be used. When they are no longer needed, they can be disconnected again. Plug and play does not require the user to load a specific device driver to access the device.
Plug and play is used to refer to both the configuration of devices at boot time, as well as to system that support adding a device later on. Examples for systems that support plug and play are USB and Firewire.